I'm stilll not convinced you 'need' s-h AF to do action photography, or photography of any kind. It's just that some who know little but are dependent upon it. Accordingly, there are expectations.
No, Pentax is not where I'd go for tracking race cars. Who said you had to, anyway. I got curious and shot oncoming objects out a moving car window recently, just out of curiosity: brick buildings at middle range with us going about 35. Seemed to work, to me. I think the most disconcerting thing about it was not *knowing* if it worked till I chimped.
I would not believe the 'can't.' It might not be what I'd pick for a job, but people say it like you can't sit in the stands and have your fun and get your shots. This just isn't true.
When autofocus first was being sold in a consumer form, we used to race me against it in a shop, simple test, me vs Maxxums and Nikons turning and shooting at a clock someone held at unknown range. My K20d could beat me now, maybe could have even beat me then.....the weak link's long been 'Tell the camera what to lock onto.' ...*then* how fast it is gets involved.
Yeah, if you were doing it for a living, you'd want it as fast as you could get: I'm certainly not getting any faster, myself: I'l take faster, as long as I don't lose accuracy in the bargain. But I don't buy vehicles based on the idea I 'can't' get to a campsite or park on an unpaved lot without the latest four wheel drive, either.
Photography, even action photography, though, if you asked me, isn't about speed, it's about, 'how fast can you take your time?'
How fast can you be steady and accurate and get the shot. Some machines are more optimized for that, but they can't take your photos for you.
Some makers' AF may be faster, but not faster-enough that I can afford to whiff the *exposure* cause I couldn't afford a model with two dials.